1. Field of the Invention
The present invention relates to an apparatus for providing temporary stability and floatation to marine or water borne structures (“structures”).
More particularly, the invention relates to: (1) a removable apparatus that can be temporarily attached to a structure such as a tension leg platform during the construction, transportation, installation and/or removal of the structure, where the device increases the stability of the structure by increasing its area at the water line; (2) structures having the apparatus(es) or modules attached thereto; and (3) method for using the modules during the construction, transportation, installation and/or removal of the structure.
2. Description of the Related Art
It is widely known and long established that significant and valuable natural resources are located on or beneath the ocean floor or other large bodies of water. This environment creates numerous obstacles or challenges to the exploration, mining or other collection of these resources.
Hydrocarbon liquids and gases trapped below the ocean floor are one of the most common and best known resources that are collected or mined. This mining and collection process has resulted in the construction of large offshore drilling, production, and utility platforms. Variations of platform design and construction have evolved. The earliest platforms were mounted on tall structures attached to the ocean floor. As the exploration of hydrocarbon fuels has progressed into deeper waters or more hostile environments, other platform designs have evolved, e.g., spar, single column floater (SCF) platform structures, and tension leg platform structures.
The cost and difficulty in constructing these structures are significantly diminished when the major portion of construction and assembly of the structure, the attached platform, ancillary equipment, and facilities, is accomplished at or near a shoreline fabrication site. In contrast, construction and assembly at or near the final ocean installation site, is often far removed from the necessary supply base and subject to inclement weather conditions.
Many common types of offshore platforms cannot be fabricated in their entirety at or near shore due to a variety of limitations. A spar platform typically has a large draft, which requires fairly deep water, i.e., greater than approximately 150 meters in its final vertical orientation. The spar platform is, therefore, generally transported on its side without associated equipment or ancillary facilities to the installation site. Offshore construction is required after the platform is upended to its vertical orientation to complete the facility. The cost of offshore construction is substantially greater than construction at an onshore facility. Alternate, devices or methods require the structure to be tilted along its vertical axis to control the structure's stability during installation.
Tension leg platforms (TLPs) can and have been fabricated in their entirety at or near shore and towed as a complete platform to the installation site. However, the efficiency of the platform is compromised because the structure must be designed to be satisfactorily stable at a much shallower draft than the design installed draft. Adequate stability requires larger columns or wider column spacing than would be required for the operation of the structure after installation. Both features, i.e., construction of larger columns or placement of columns at wider intervals, add significant costs to the structure.
Recent advancements in tension leg platforms include single column and extended base varieties. A complete single column tension leg platform, including the platform, deck, equipment and related facilities cannot be constructed at or near shore, because the structure is not stable about its vertical axis until after tendon installation is complete. If the structure is constructed on its side at a shore fabrication site, the ancillary deck, equipment and facilities cannot be constructed until the structure is righted, tendons attached and installation completed. Moreover, these alternate designs for tension leg platform are more efficient when designed and constructed to provide stability only after tendons attachment.
Many devices and techniques have been described in the prior art for transporting structures to an offshore installation site. Many have related to the placement of the structure on its side and floating it to the site. The structure can then be then placed in the final upright position by various techniques such as controlled flooding of the structure or removal of floatation devices. Other devices or techniques have utilized the tipping of the structure during the installation process in order to facilitate stability during installation. Examples of such prior art are found in U.S. Pat. Nos. 3,811,681, 3,823,564, 3,859,804, 3,868,886, 4,062,313, 4,112,697, 4,385,578, 4,648,751, 4,768,456, 4,809,636, 4,811,681, 4,874,269, 4,913,591, 5,224,962, 5,403,124, 5,524,011, and 5,924,822, incorporated herein by reference. However, these devices and/or techniques do not permit the structure, including but not limited to the ancillary platform, deck, equipment and other facilities to be constructed in its final installation orientation, transported to the installation site and installed and secured without tipping the structure or permanently incorporating additional physical elements into the structure that permit such construction, transportation and installation.
Thus there is a need in the art for a device and method that allows the structure to be constructed, transported, installed and later removed in a substantially upright orientation.